ITU-R REPORT BT.1209 [ Active ]

INTRODUCTION

With the advent of digital picture processing, the problems of spurious radiation from such apparatus has had to be considered.Equipment built to operate on the CCIR Recommendation 601 digital video standard utilizes a luminance sampling frequency of 13.5 MHz, the ninth harmonic of which coincides exactly with an international distress frequency, namely 121.5 MHz. In addition, 243 MHz, or the 18th harmonic of the luminance sampling frequency, is also reserved for international distress use.

The international distress frequencies, 121.5 MHz and 243 MHz are used by Emergency Location Transmitters (ELT) in the aeronautical service and Emergency Position Indicating Radio Beacons (EPIRB) in the marine service. The methods of operation are similar and an emergency is indicated by the radiation of a carrier with AM "chirp" modulation. The signals may be received on fixed receivers but are usually detected by aircraft or satellite receivers. Sophisticated processing is required to detect these signals reliably due to noise, interference and frequency variations due to misalignment and Doppler shifts over a bandwidth of 25 KHz. [Chung and Carter, 1987] outlines the processing involved in the SARSAT (Search And Rescue Satellite Aided Tracking) program of Canada, USA, France and USSR.

In view of the need to eliminate harmful interference, the design, construction and operation of digital equipment must take this into consideration, as a high priority. This report describes electrical and mechanical measures, methods of measurement and some results of measurement.